The signals received and transmitted in wireless communications systems often vary in strength and thus require the use of variable gain amplifiers in the radio transceiver. These variable gain amplifiers operate to remove fluctuations in the received signal and to compensate for path losses in the transmitted signal.
Ideally, the variable gain amplifier (VGA) provides amplification at low noise levels, adds little distortion, and consumes very little power. This is important because distortion produced by the receiver VGA limits its ability to reject interfering signals, while distortion produced by the transmitter VGA spills power into adjacent communication channels and thereby reduces system capacity. To minimize distortion, the bias current in the VGA and other circuits is typically high—an unwanted attribute for portable devices.
It would therefore be advantageous to have a VGA with low distortion and low power consumption.